In the world, but not of it

Of the many tensions that we are dealing in the Christian life, this is one of those that receives something of a special spot, because it is introduced in John's Gospel by Jesus Himself in John 17. By any standard, this speaks against a withdrawal in cozy Christian subcultures, and asks for engagement with the world around us.
Karl Barth had something to say to this point in his own way, speaking about church and world:

"In both spheres there are human words which are good because they are spoken with the commission and in the service of God. In both spheres there are words which are illuminating and helpful to the degree that God Himself gives it to them to be illuminating and helpful as such words." (CD IV/3, §69)